The invention relates to an improved pressure filter having a casing with a filter arranged therein having a filter material carrier and a conveyor. The conveyor is located on an arm that is axially displaceable and rotatable about a vertical axis. Filter cake that is collected on the filter is conveyed into a centrally, downwardly directed discharge pipe.
Pressure filters of this type are known as nutsch filters and are used for separating suspensions that can be moderately or easily filtered. Such a nutsch filter is described, for example, in Swiss Pat. No. 441,230. In the patent there is shown a nutsch filter having a casing with at least one filter material carrier arranged therein. With the aid of a separate conveyor, the filter cake collected on the filter is conveyed into a discharge pipe arranged concentrically to the vertical casing axis. The discharge pipe is connected to the conveyor in such a way that the pipe necessarily participates in all the vertical movements of the conveyor. The discharge pipe separated from the conveyor only for cleaning and inspection purposes. When such filters are used as nutsch filters, the lower end of the discharge pipe is tightly sealed during the suction filtration process, so that no filter mass can run out. On initially charging filter mass into the pressure filter, as a result of accidental overfilling of the device, filter mass can pass into the upper free opening of the discharge pipe and cause stoppages. In addition, the relatively large volume of the discharge pipe has a disadvantageous effect during suction filtration, because the air contained therein is compressed and leads to difficultly controllable pressure conditions. This compression is disadvantageous because the air volume of the discharge pipe is of the same order of magnitude as that of the remaining filter chamber.
In another known filter means described in West German Offenlegungsschift No. 31 36 773, the lower end of the discharge pipe is closed by a valve, but this point on the pipe is exposed to a high degree of contamination and, due to the filter cake residues deposited there, often leads to stoppages. In this known filter means, paring or skimming knives are provided on a rotary arm and pare or skim the solidified filter cake outwards or in arrow-like manner to either side, so that, as a function of the alignment of the rotating knives, the material is either thrown outwards or to either side of the knives. The piled-up filter mass must then be conveyed to the central removal opening on the filter in a separate operation, while reversing the rotation direction of the arm and using transfer blades, which are also fixed to the arm, but are functionally separated from the knives.
Apart from such nutsch filters providing for central discharge of the filter cake, nutsch filters are known providing for a lateral discharge of the filter cake, particularly using screw conveyors. Although known nutsch filters of this type have proved basically satisfactory in operation, they need improvement on the basis of modern constructional ideas, particularly for facilitating the operation and maintenance of the system. The screw conveyors have proved particularly complicated and prone to faults.